1. Field of the invention
The present invention relates to a flexible housing for use in protecting one or more transmission lines, particularly microwave transmission lines, in a pressurized environment and, in particular, a hydrostatically pressurized environment.
2. Description of Related Art
The invention originates from a requirement for a microwave transmission line to operate within a submarine mast environment. Modern submarine mast design dictates the placement of electronic equipment in an electronics pod at the mast head connected by microwave transmission lines to processing equipment in the hull. This arrangement creates the requirement for a microwave transmission line capable of withstanding a hydrostatic pressure of up to 1000 psi (6.89.times.10.sup.6 Nm.sup.-2) and yet be able to flex through an angle of 180.degree. with a bend radius of 150 mm when the mast head is raised.
In the past, various "wet mast" techniques have involved the ruggedising of coaxial microwave cables so as to limit an acceptable level the amount of hydrostatic pressure felt by the cable. Often, under such pressure conditions, it is the dielectric within the coaxial cable that absorbs the bulk of the compressive forces, altering the microwave characteristics of the cable.
The use of a more rigid dielectric material to overcome the problem of compression under hydrostatic pressure has an adverse effect on cable performance. Furthermore, this technique limits the types of cable which can be used, their number and their application, and consequently, has a detrimental effect on the performance of the system as a whole.
The above technique also requires the use of some form of cable management system to ensure that the cables hang and remain in a defined position under the various dynamic conditions of the submarine. Each microwave transmission line linking the electronics pod at the mast head with the processing equipment in the hull will contain a flexure through 180.degree., the point of flexure being determined by the relative heights of the terminations of the transmission line; and the point of flexure will thus change as the mast is raised. The cable management system not only has to allow for the smooth change in position of the point of flexure, but also has to ensure that the transmission lines are unaffected by the angle of dive of the submarine, which may be of the order of .+-.10.degree., or the angle of tilt of the submarine caused by a surface swell and possibly of the order of .+-.30.degree..
The present invention is concerned with the provision of a barrier between a pressurized environment and a microwave transmission line thus enabling the use of cables selected for their microwave characteristics rather than their ability to withstand hydrostatic pressure. This is obviously beneficial to the performance of the system while the barrier, in the form of a flexible housing, enables the transmission line to withstand far greater hydrostatic pressures than heretofore. The design of the present invention also eliminates the need for a cable management system, thus simplifying the mast design.